This invention relates generally to a system for storing a quantity of continuous strip material such as tape or film. More particularly, the invention describes a method and apparatus for continuously storing motion picture film on edge on a flat rotating platter, as part of an endless loop film projection system.
It has long been recognized in motion picture projection that an endless loop system is desirable, in order to eliminate the need for manual rewinding and rethreading of film in repeated renditions of a program. A number of attempts have been made to provide for storing the film in a coil on a rotating turntable or platter in such a way as to minimize relative longitudinal movement between adjacent film layers in the coil, and yet permit, during each platter revolution, a predetermined length of film to be withdrawn from the center of the coil while the identical length of film is being added to the outside of the coil. The prior systems produce a series of angularly spaced, inwardly directed rounded cusps in the film coil, and are exemplified by the two U.S. patents to Johnson, U.S. Pat. Nos. 4,066,221 and 4,186,891, the U.S. Pat. No. 4,208,018 to Wilkinson, and the U.S. Pat. No. 4,504,025 to Potts. These patents, in common with other prior systems include an application apparatus for incoming film which feeds or applies the incoming film to the rotating platter and means for shaping the film in the coil into a number of spaced inwardly directed cusps.
In another apparatus, the strip or film is transported from the edge of the platter toward the center of the coil by the tension of the strip in the outer layers. A cam is carried for rotation with the platter, with the cam having alternating sections of greater distance and lesser distance from the center, typically comprising arcuate sections and chord sections, respectively. The strip is applied to the outer periphery of the coil by a mechanism which includes a cam follower riding on the cam track as the platter rotates. This apparatus provides the desired cusps in the coil of film, but also involves an undesired tensioning of the film with a resultant rubbing of one layer of film against the adjacent layer. This operation is illustrated in FIG. 14. A white chalk line 20 was applied as a straight line or radius on a coil 21 of film resting on a platter 22. This line 20 was extended to the outer periphery of the coil and an index line 23 was applied at the edge of the platter 22 aligned with the line 20. The apparatus was then operated in the normal manner for ten minutes resulting in application of additional film indicated at 24. The slippage of one layer of the film strip relative to the next during the film application is demonstrated by the curve in the line 20.
Motion picture film has a tendency to curl when a length of the film is in an unwound strip condition; as is the case when film is moving from the projector to the coil on the platter. Curling is a problem caused by the change in dimension of the emulsion side of the film with respect to the base side of the film and is exaggerated by changes in such things as temperature and humidity.
Accordingly, it is an object of the present invention to provide a new and improved method and apparatus for continuously storing a strip of material in a coil and incorporating the advantages of the prior cam and cam follower system, while overcoming the disadvantages thereof. A particular object of the invention is to provide such a method and apparatus including means for relieving tension in the applied strip, as by addition of a pressure roller for contacting the arcuate periphery of the coil and urging it inward. The pressure roller may contact the coil only at a fixed radius or may contact the coil continuously.
It is a further object of the invention to provide an improvement in film handling systems by controlling the friction of the coil on the platter and more particularly by providing a continuous friction producing surface on the platter at the arcuate sections thereby facilitating cusp formation and enhancement. The friction producing surface may have an elevated outer contour to aid in developing the arcuate shape of the coil.
It is another object of the invention to achieve a further improvement in film handling by providing a skid or low friction surface on the platter in the cusp sections of the coil with such surface having an elevated inner contour corresponding to the desired cusp configuration.
It is an object of the invention to provide a new and improved cam track and cam follower construction for control of the application of the strip to the coil including pressure roller and application roller position control, drive mechanism and/or platter and cam track configuration.
Another problem encountered with prior art systems is the positioning of the strip at the center of the coil during takeoff, and control of the strip immediately after its removal from the inside of the coil. In prior art configurations, the takeoff guide, typically a takeoff roller or set of rollers, is positioned at the center of the coil and limits the motion of the strip during takeoff. It is an object of the present invention to provide an improvement on this configuration and in particular, to position a takeoff roller assembly above and spaced from the coil at the center of the coil thereby doing away with restrictions on strip movement.
These and other objects, advantages, features and results will more fully appear in the course of the following description.